An unneccessary demonstration of the obvious, "The Legend of the Lone Ranger" confirms that it is not only absurd but also cruel to revive slumbering western heroes like the Lone Ranger and Tonto. If any lingering appeal flickered in the outmoded, campy figures of The Masked Man and His Faithful Indian Companion, this fractured epic should extinguish it for a century or two.

At a Kennedy Center invititational preview last weekend, an audience dominated by elderly buckaroos whooped it up whenever the movie evoked a familiar cliche: the first appearance of the hero in his mask; the sound of the William Tell Overture; catch lines like "Hi-yo, Silver, away!" or "Who was that masked man?" Indeed, "Legend" may be a cult turkey for oldtimers.

Unfortunately, there's no compelling reason for moviegoers a generation or two younger to get similarly carried away. If anything, the most pertinent question for uninitiated customers is likely to be, "Who are these hopeless amateurs?"

The most exposed amateur is Klinton Spilsbuy (a name W.C. Fields would have loved) as John Reid, who assumes the disguise of the Lone Ranger after surviving an ambush that wipes out a Texas Ranger posse led by his brother. A tall, handsome, histrionically helpless hunk, Spilsbury was probably cast on the strength of his resemblance to Christopher Reeve, who rationalized the big gamble of "Superman" by proving an expert light comedian, too.

The brain trust behind "Legend" must have missed the point: Reeve wasn't just a good-looking find; he was also an actor. Obviously an untrained pretty face, Spilsbury suffers the goofy consequences -- he looks like a big buffoon up there. Even his voice was inadequate, necessitating dubbing assistance by actor James Keach. Not that the cryptic dialogue is especially eloquent to begin with. The only aspect of Spilsbury's performance that carries conviction is the pained look on his face during a grotesque slow-motion sequence in which the Lone Ranger sits astride the bucking Silver.

At the same time, it's illogical of the producers to dub Spilsbury while permitting Michael Horse, the demure new Tonto, and Juanin Clay, a stupefying new ingenue cast as the Ranger's lady fair, Amy Striker, to muddle through on their own faulty equipment. In fact, Clay is a more consistent hoot than the struggling young men. They should be thankful she's around to take some of the heat off.

An astute scenario might have led off with the ambush. A veteran posse of screenwriters -- Ivan Goff, Ben Roberts, Michael Kane and William Roberts are officially credited -- takes over half the movie to reach the point where John Reid becomes the Lone Ranger. This leaves barely enough time for a lone adventure, the rescue of President Grant (Jason Robards) from the outlaw gang of Butch Cavendish, a haughty fanatic played by Christopher Lloyd.

The narrative is slowed by a rambling preamble in which John Reid and Tonto are introduced as boyhood chums; Reid is sent East after the murder of his parents and then returns West as a well-meaning young dude. This roundabout heap of exposition and development may also have been conceived in ill-advised imitation of the beginning of "Superman."

The childhood prologue begins in confusion, as two bad hombres intent on butchering young Tonto take a sudden detour and end up burning down the Reid ranch. The orphan boy is sheltered breifly by Tonto's tribe, but the sequence is too perfunctory is establish the idea of enduring friendship. In fact, much of the narrative load is shifted to an endless ballad composed by Merle Haggard, who keeps returning to update the action in excruciating verse. Sample couplet: "Tonto held onto a fervent hope/That The Masked Man wouldn't let his blood brother hang by the end of a rope."

Every so often one suspects the presence of a cynical saboteur on the writing staff. During a stagecoach ride across Monument Valley, for example, a German immigrant passenger enthuses over "America, the land of opportunity." Moments later the stage is attacked by masked bandits, and while the passengers sit around, a stay bullet kills the immigrant. "So much for American opportunity," cracks a fellow passenger.

"The Legend of the Lone Ranger" is not the kind of foolproof entertainment that can afford a little intramural funning. Indeed, I suspect that the Kennedy Center preview may have been its first and last hurrah. The long-term prospects for this sagebrush laughter are not auspicous -- probably three weeks and a cloud of dust followed by a hearty "Hi, there, HBO!"